The present application claims priority to Korean Patent Application No. P2000-69658 filed on Nov. 22, 2000, the disclosure of which is hereby incorporated into the present application by reference.
The present invention relates to a semiconductor device, and more particularly, to a method for fabricating a capacitor of a semiconductor device that prevents a lower electrode from being oxidized, thereby improving a leakage current characteristic of the device.
It is known to densely pack DRAM modules on a semiconductor device to achieve a desired capacitance. However, the size of the DRAM and the area of the capacitor must be reduced to achieve the desired density. A Ta2O5 film that can obtain high capacitance in a relatively small area can be used as a dielectric film for such a capacitor.
When the Ta2O5 film is used as the dielectric film, silicon can be used as a lower electrode of the capacitor. However, a doping concentration of the silicon can adversely lower the capacitance of the capacitor.
A capacitor having a metal-insulator-metal (MIM) structure can be used to avoid this disadvantage. In the MIM structure, a lower electrode is formed of a metal. In particular, it is known to form the lower electrode from tungsten (W).
FIGS. 1A to 1E show cross-sectional views of a known method for fabricating a capacitor of a semiconductor device.
As shown in FIG. 1A, a first tetra ethyl ortho silicate (TEOS) film 12 and a first nitride film 13 are sequentially deposited on a semiconductor substrate 11. An oxidation process that uses O2 is performed.
Subsequently, the first nitride film 13 and the first TEOS film 12 are selectively removed by photolithography and etching processes to form a contact hole 14 that exposes a portion of the semiconductor substrate 11.
A second nitride film is deposited on a surface of the semiconductor substrate 11 and then etched back such that the nitride film remains on a sidewall within the contact hole 14 to form nitride film spacers 15.
As shown in FIG. 1B, a polysilicon film is deposited on the entire surface of the semiconductor substrate 11 and into the contact hole 14. The polysilicon film is then etched back to form a plug 16 that is disposed within the contact hole 14.
Subsequently, a second TEOS film 17 is deposited at a predetermined thickness and then selectively removed by the photolithography and etching processes, thereby forming a trench 18 that exposes the plug 16 and a surface of the first nitride film 13 adjacent to the plug 16.
As shown in FIG. 1C, a tungsten film 19 is formed by a sputtering method and a chemical vapor deposition (CVD) method. A surface of the tungsten film 19 formed by the CVD method is very rough.
A third TEOS film 20 and a spin on glass (SOG) film 21 are sequentially deposited into the trench 18. The SOG film 21 and the third TEOS film 20 are selectively removed by an etch-back process to expose a surface of the tungsten film 19 disposed outside of the trench 18.
As shown in FIG. 1D, the exposed tungsten film 19 is removed by a CMP process. The unexposed tungsten film 19 within the trench 18 constitutes a lower electrode 19a. 
The remaining SOG film 21 and third TEOS film 20 are removed by a wet etching process.
As shown in FIG. 1E, the second TEOS film 17 is removed by the photolithography and etching processes.
A Ta2O5 film 22 is deposited on the surface of the semiconductor substrate 11. The Ta2O5 film 22 is then oxidized by a low temperature ultraviolet (UV)-ozone (O3) process. The process uses light having a wavelength of between about 250 to about 260 nm that is generated by an UV-lamp to irradiate O3 produced by an O3 generator. However, the lower electrode 19a disposed below the Ta2O5 film 22 is also oxidized by this process. The UV-O3 process is performed at a low temperate to reduce the degree of oxidation of the lower electrode 19a. 
A titanium nitride (TiN) film or a tungsten(W) film is used as the metal film for an upper electrode. The tungsten film is selectively removed by the photolithography and etching processes such that the film remains on the Ta2O5 film 22 disposed on the lower electrode 19a and remains on a region adjacent to the lower electrode 19a to form an upper electrode 23. Thus, a capacitor of a known semiconductor device is fabricated.
FIG. 2 shows the surface of the lower electrode formed of tungsten. The upper portion of the lower electrode 19a was formed by the CVD method. The lower electrode 19a and the Ta2O5 film were oxidized during the UV-O3 oxidation process. As shown in the figure, the surface of the lower electrode 19a is relatively very rough.
The high surface roughness of the lower electrode 19a results in a relatively high application of an electric field at discreet portions of the electrode. The conventional method for fabricating a capacitor of a semiconductor device results in several disadvantages.
Since both the lower electrode as well as the Ta2O5 film are oxidized during the oxidation process of the Ta2O5 film, a leakage current is increased due to a tunneling of electrons, as shown in FIG. 3. Because the UV-O3 process is performed at a low temperature to reduce oxidation of the lower electrode, an oxidation efficiency and therefore electrical characteristics of the Ta2O5 film are also decreased.
The invention provides a method for fabricating a capacitor of a semiconductor device on a semiconductor substrate that prevents a lower electrode from being oxidized, thereby improving a leakage current characteristic of the device. An insulating film can be formed on the semiconductor substrate. A plug can be formed in the insulating film, the plug electrically connected with the semiconductor substrate. A lower electrode can be formed on the plug and the insulating film adjacent to the plug. A Ta2O5 film can be formed on the lower electrode and the insulating film adjacent to the lower electrode. The Ta2O5 film can be oxidized by flowing oxygen under the ambient of hydrogen gas at a temperature of between about 800xc2x0 C. and 850xc2x0 C. An upper electrode can be formed on the Ta2O5 film on the lower electrode and the insulating film adjacent to the lower electrode.
Additional advantages and features of the invention will be set forth in part in the description which follows, and in part will become apparent to those having ordinary skill in the art upon examination of the following, and/or can be learned from practice of the invention. The advantages of the invention may be realized and attained as particularly pointed out in the appended claims.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, a method for fabricating a capacitor of a semiconductor device according to the invention can include the steps of forming an insulating film on a semiconductor substrate; forming a plug electrically connected with the semiconductor substrate through the insulating film; forming a lower electrode on the plug and the insulating film adjacent to the plug; forming a Ta2O5 film on a surface of the semiconductor substrate; oxidizing the Ta2O5 film by flowing oxygen under the ambient of hydrogen gas of 800xc2x0 C. to 850xc2x0 C.; and forming an upper electrode on the Ta2O5 film over the lower electrode and a region adjacent to the lower electrode.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.